It said during painting and maintenance it was important to protect all aerodynamic data sensors.
It has also said that tests such as low speed tests "must be performed at safe altitude and be preceded by a recall of basic rules as regards to minimum speeds and recovery actions".
When trapped water in a static system freezes during flight, above that freeze altitude the ASI will underread (and below that height it will overread - dangerous wrt (to) stall speed). Altimeters may freeze and VSI will......
Of course it all depends upon how many static ports there are - and how they're plumbed in to air data.....